Allow builtin language servers to be disabled by default (#65049)

## Summary

This addresses the concern mentioned in
https://github.com/zed-industries/zed/pull/65030#pullrequestreview-5380076060

Release Notes:

- N/A

crates/edit_prediction_context/src/fake_definition_lsp.rs

@@ -34,7 +34,7 @@ pub fn register_fake_definition_server(
                 arguments: Vec::new(),
                 env: None,
             },
-            enabled_by_default: true,
+            opt_in_languages: Default::default(),
             capabilities: lsp::ServerCapabilities {
                 definition_provider: Some(lsp::OneOf::Left(true)),
                 type_definition_provider: Some(lsp::TypeDefinitionProviderCapability::Simple(true)),

crates/language/src/language.rs

@@ -334,7 +334,6 @@ pub struct CachedLspAdapter {
     pub disk_based_diagnostic_sources: Vec<String>,
     pub disk_based_diagnostics_progress_token: Option<String>,
     language_ids: HashMap<LanguageName, String>,
-    pub enabled_by_default: bool,
     pub adapter: Arc<dyn LspAdapter>,
     cached_binary: Arc<ServerBinaryCache>,
 }
@@ -352,7 +351,6 @@ impl Debug for CachedLspAdapter {
                 &self.disk_based_diagnostics_progress_token,
             )
             .field("language_ids", &self.language_ids)
-            .field("enabled_by_default", &self.enabled_by_default)
             .finish_non_exhaustive()
     }
 }
@@ -363,14 +361,12 @@ impl CachedLspAdapter {
         let disk_based_diagnostic_sources = adapter.disk_based_diagnostic_sources();
         let disk_based_diagnostics_progress_token = adapter.disk_based_diagnostics_progress_token();
         let language_ids = adapter.language_ids();
-        let enabled_by_default = adapter.enabled_by_default();
 
         Arc::new(CachedLspAdapter {
             name,
             disk_based_diagnostic_sources,
             disk_based_diagnostics_progress_token,
             language_ids,
-            enabled_by_default,
             adapter,
             cached_binary: Default::default(),
         })
@@ -380,6 +376,12 @@ impl CachedLspAdapter {
         self.adapter.name()
     }
 
+    /// Returns whether the language server only starts for the given language
+    /// when it is explicitly listed in the `language_servers` setting.
+    pub fn is_opt_in_for(&self, language: &LanguageName) -> bool {
+        self.adapter.is_opt_in_for(language)
+    }
+
     pub async fn get_language_server_command(
         self: Arc<Self>,
         delegate: Arc<dyn LspAdapterDelegate>,
@@ -660,10 +662,11 @@ pub trait LspAdapter: 'static + Send + Sync + DynLspInstaller {
         HashMap::default()
     }
 
-    /// Whether the `...` wildcard in the `language_servers` setting includes this
-    /// language server. If `false`, it only starts when listed explicitly.
-    fn enabled_by_default(&self) -> bool {
-        true
+    /// Whether the `...` wildcard in the `language_servers` setting excludes this
+    /// language server for the given language, so that it only starts when
+    /// listed explicitly.
+    fn is_opt_in_for(&self, _language: &LanguageName) -> bool {
+        false
     }
 
     /// Support custom initialize params.
@@ -933,7 +936,7 @@ pub struct FakeLspAdapter {
     pub disk_based_diagnostics_progress_token: Option<String>,
     pub disk_based_diagnostics_sources: Vec<String>,
     pub language_server_binary: LanguageServerBinary,
-    pub enabled_by_default: bool,
+    pub opt_in_languages: HashSet<LanguageName>,
 
     pub capabilities: lsp::ServerCapabilities,
     pub initializer: Option<Box<dyn 'static + Send + Sync + Fn(&mut lsp::FakeLanguageServer)>>,
@@ -1561,7 +1564,7 @@ impl Default for FakeLspAdapter {
                 arguments: vec![],
                 env: Default::default(),
             },
-            enabled_by_default: true,
+            opt_in_languages: HashSet::default(),
             label_for_completion: None,
         }
     }
@@ -1664,8 +1667,8 @@ impl LspAdapter for FakeLspAdapter {
         label_for_completion(item, language)
     }
 
-    fn enabled_by_default(&self) -> bool {
-        self.enabled_by_default
+    fn is_opt_in_for(&self, language: &LanguageName) -> bool {
+        self.opt_in_languages.contains(language)
     }
 
     fn is_extension(&self) -> bool {

crates/language_extension/src/extension_lsp_adapter.rs

@@ -305,12 +305,12 @@ impl LspAdapter for ExtensionLspAdapter {
             .unwrap_or_default()
     }
 
-    fn enabled_by_default(&self) -> bool {
+    fn is_opt_in_for(&self, language: &LanguageName) -> bool {
         self.extension
             .manifest()
             .language_servers
             .get(&self.language_server_id)
-            .is_none_or(|server| !server.is_opt_in_for(&self.language_name))
+            .is_some_and(|server| server.is_opt_in_for(language))
     }
 
     async fn initialization_options(

crates/languages/src/python.rs

@@ -372,6 +372,10 @@ impl LspAdapter for TyLspAdapter {
         Self::SERVER_NAME
     }
 
+    fn is_opt_in_for(&self, language: &LanguageName) -> bool {
+        language == "Python"
+    }
+
     async fn label_for_completion(
         &self,
         item: &lsp::CompletionItem,
@@ -665,6 +669,10 @@ impl LspAdapter for PyrightLspAdapter {
         Self::SERVER_NAME
     }
 
+    fn is_opt_in_for(&self, language: &LanguageName) -> bool {
+        language == "Python"
+    }
+
     async fn initialization_options(
         self: Arc<Self>,
         _: &Arc<dyn LspAdapterDelegate>,
@@ -1816,6 +1824,10 @@ impl LspAdapter for PyLspAdapter {
         Self::SERVER_NAME
     }
 
+    fn is_opt_in_for(&self, language: &LanguageName) -> bool {
+        language == "Python"
+    }
+
     async fn process_completions(&self, items: &mut [lsp::CompletionItem]) {
         for item in items {
             let is_named_argument = item.label.ends_with('=');

crates/languages/src/typescript.rs

@@ -875,6 +875,10 @@ impl LspAdapter for TypeScriptLspAdapter {
             (LanguageName::new_static("TSX"), "typescriptreact".into()),
         ])
     }
+
+    fn is_opt_in_for(&self, language: &LanguageName) -> bool {
+        matches!(language.as_ref(), "TypeScript" | "JavaScript" | "TSX")
+    }
 }
 
 async fn get_cached_ts_server_binary(

crates/project/src/manifest_tree/server_tree.rs

@@ -253,7 +253,7 @@ impl LanguageServerTree {
         let available_lsp_adapters = self.languages.lsp_adapters(language_name);
         let available_language_servers = available_lsp_adapters
             .iter()
-            .filter(|lsp_adapter| lsp_adapter.enabled_by_default)
+            .filter(|lsp_adapter| !lsp_adapter.is_opt_in_for(language_name))
             .map(|lsp_adapter| lsp_adapter.name.clone())
             .collect::<Vec<_>>();
 

crates/project/tests/integration/project_tests.rs

@@ -2089,7 +2089,7 @@ async fn test_language_servers_disabled_by_default(cx: &mut gpui::TestAppContext
             "Rust",
             FakeLspAdapter {
                 name: "opt-in-server",
-                enabled_by_default: false,
+                opt_in_languages: HashSet::from_iter([LanguageName::new_static("Rust")]),
                 ..Default::default()
             },
         );

docs/src/configuring-languages.md

@@ -128,7 +128,7 @@ In this example:
 
 The `"..."` entry acts as a wildcard that includes any registered language server you haven't explicitly mentioned. Servers you list by name keep their position, and `"..."` fills in the remaining ones at that point in the list. Servers prefixed with `!` are excluded entirely. This means that if a new language server extension is installed or a new server is registered for a language, `"..."` will automatically include it. If you want full control over which servers are enabled, omit `"..."` — only the servers you list by name will be used.
 
-Extensions can also mark a language server as [disabled by default](./extensions/languages.md#opt-in-language-servers) for some of its languages. Such servers are never included by `"..."`, regardless of your configuration, and only start when you list them by name, e.g. `["my-alternative-server", "..."]`.
+Some language servers are disabled by default for some of their languages, e.g. `typescript-language-server` for TypeScript, or `ty` for Python. Extensions can also mark their language servers as [disabled by default](./extensions/languages.md#opt-in-language-servers). Such servers are never included by `"..."`, regardless of your configuration, and only start when you list them by name, e.g. `["my-alternative-server", "..."]`.
 
 #### Examples
 

docs/src/languages/python.md

@@ -80,7 +80,7 @@ Other built-in language servers are:
 - [Pyright](https://github.com/microsoft/pyright)—The basis for basedpyright.
 - [PyLSP](https://github.com/python-lsp/python-lsp-server)—A plugin-based language server that integrates with tools like `pycodestyle`, `autopep8`, and `yapf`.
 
-These are disabled by default, but can be enabled in your settings.
+These are disabled by default and are not included by `"..."`. Enable them by listing them by name in your settings.
 
 Configure language servers in Settings ({#kb zed::OpenSettings}) under Languages > Python, or add to your settings file:
 
@@ -89,8 +89,8 @@ Configure language servers in Settings ({#kb zed::OpenSettings}) under Languages
   "languages": {
     "Python": {
       "language_servers": [
-        // Enable ty, disable basedpyright, and enable all
-        // other registered language servers (ruff, pylsp, pyright).
+        // Enable ty, disable basedpyright, and enable all other
+        // language servers that are enabled by default (e.g. ruff).
         "ty",
         "!basedpyright",
         "..."